Hair growth is cyclical, occurring in three stages: anagen, the active growth phase; catagen, the degenerative phase; and telogen, the resting phase. After telogen, the old hair fibre is shed and a new hair is generated as part of the repeating cycle.
Alopecia, or hair loss, occurs in both men and women, and is attributed to numerous causes including aging, hormone levels, stress, and chemotherapy. In these circumstances, more and more hair follicles remain in the telogen stage, resulting in a gradual decrease of the hair fibre length and diameter, finally reaching a stage of partial or complete baldness.
Various types of hair loss are known, including alopecia areata, androgenetic alopecia, anagen effluvium, self-induced hair loss, telogen effluvium, and scarring alopecia. Alopecia areata, thought to be an auto-immune disorder, begins with hair loss in a rounded patch on the scalp. Alopecia areata includes mild patchy hair loss on the scalp, as well the loss of all scalp hair, known as alopecia totalis, and the loss of all scalp and body hair, known as alopecia universalis. Androgenetic alopecia, including male and female pattern baldness, is thought to be caused by a combination of genetic predisposition, aging, and androgen hormone levels. Androgenetic alopecia is associated with increased androgen stimulation, which adversely affects the hair follicles.
Increased androgen stimulation can be produced by, among other mechanisms, elevated levels of 5-alpha-reductase, an enzyme that converts testosterone to dihydrotestosterone. Anagen effluvium is hair loss due to chemicals or radiation, such as chemotherapy or radiation treatment for cancer. Self-induced hair loss includes hair loss caused by conscious or unconscious self-inflicted damage to the hair. Two common types of self-induced hair loss are trichotillomania, or hair loss that results when someone continually pulls or plucks out his own hair, and traction alopecia, which is caused by hairstyles such as ponytails or braids that continually pull at the hair. Telogen effluvium is stress-related hair loss caused by events such as, for example, surgery, child birth, or pregnancy termination. Further causes of telogen effluvium include the use of oral contraceptives or other prescription drugs, thyroid abnormality, diabetes, lupus, and emotional stress. Scarring alopecia includes hair loss caused by infection and inflammation of the hair follicles, and hair loss caused by burns or other trauma.
Hair loss is a widespread problem that is considered by some to be cosmetically unappealing and often causes emotional distress to the individual concerned. As a consequence, there is great demand for alopecia treatments. Many compositions have been tested for their ability to stimulate hair growth, for example, by promoting or prolonging anagen. Examples of such compositions include potassium channel openers, such as minoxidil (Regaine®, Pharmacia Corp.) and diazoxide; 5-alpha-reductase inhibitors, such as finasteride (Propecia®, Merck & Co.); and the immunosuppressant cyclosporin A.
However, such known treatments for stimulating hair growth exhibit limited effectiveness and cause unwanted side effects. For example, among other undesirable side effects, potassium channel openers cause cardiovascular effects, finasteride is unsafe for women who are pregnant or may become pregnant, and cyclosporin A suppresses the immune system. Further, even when applied topically to areas in which hair growth is desired, known treatments for alopecia often cause hair growth in undesired areas of the body, such as facial hair on women. Such disadvantages of known compositions for treating alopecia lead many individuals experiencing hair loss to rely on wigs and toupees. Other individuals seek hair transplant surgery, which is expensive, is not fully effective, and sometimes is not possible, for example, for chemotherapy patients.
Accordingly, there is a need for new treatments to stimulate hair growth, suitable for use in both medical and cosmetic applications.